Q4 2017 Refactor

• Polymer 1.x/2.x hybrid support
• Added required property and bound down to fields
• Component can now have empty state if fromMoment and toMoment are not specified
• range property no longer exists, use fromMoment and toMoment as the source of truth - this fixes the flickering / multiple events fired when any of the three were updated before
• Updated min and max to minDate and maxDate to align with field
• Added _tempFromMomentObj and _tempToMomentObj to store working copies of moment objects for validation before they get submitted/applied to the regular fromMoment / toMoment
• Updated tests